Twister technology can recover significantly more NGL than a turbo-expander and JT system without the use of hydrate inhibition chemicals.
Whereas the hydrate formation temperature limits the operating temperature in the LTS for a turbo-expander and JT system, the hydrate formation temperature only limits the Twister system at the inlet of the Twister tube. No hydrate formation takes place inside the Twister tube due to the very short residence time, and hydrates in the secondary outlet of the Twister tube are managed in the Hydrate Separator using heat input. In other words, the minimum acceptable temperature in the LTS for a turbo-expander and JT system is more or less the same as the minimum acceptable temperature at the Twister tube inlet. Therefore Twister is able to expand much deeper into the phase envelope and recover significantly more NGL than a turbo-expander and JT system without the use of hydrate inhibition chemicals.
An independent study to compare the NGL recovery rate of Twister and a JT system has been conducted by Genesis Oil & Gas covering a wide range of water contents, gas compositions and operating conditions.
The recovery rates for LPG, condensate and C3+ have been presented in figure 1 and figure 2.
Figure 1: C3+ recovery as function of water content for Twister and JT-LTS
Figure 2: NGL recovery as function of water content for Twister and JT-LTS using a chiller
This study clearly showed that Twister recovers significantly more NGLs down to very low water contents. The JT system can utilise the maximum possible heat integration at these very low water contents, without hydrate formation in the LTS, hence improving the NGL recovery rate, but the NGL recovery rate for the Twister system is still better even at these water contents.
By applying a chilled water and/or a mechanical refrigeration unit the Twister inlet temperature can be reduced again to just above the hydrate formation temperature. As expected, this results in a further increase in the NGL recovery as is presented in figure 2. The Twister C3+ recovery increases by approximately 10% (from 50-60% range to 60-70% range) when upstream chilling is applied. The JT-LTS system does not benefit from adding a chiller, since its heat integration is limited by the water in the gas. The same results can be expected for non bone-dry gas applications, where Twister is compared to a turbo-expander, as the water content will limit its LTS temperature.